The present invention relates generally to the manufacture of silicone foam and, more particularly, to the manufacture of silicone foam utilizing a reusable mechanical foaming agent.
Prosthetic devices are used for a number of purposes at various locations in the body. Many of these devices are implantable. One of the most common uses has been for augmenting or reconstructing the female breast. An example of a common breast prosthesis is disclosed in, for example, U.S. Pat. No. 3,293,663 to Cronin.
The Cronin prosthesis includes a flexible elastomeric container or envelope, typically formed from silicone that is filled with a soft gel, typically silicone gel or a saline solution or a combination of both.
It has been found that smooth envelope surfaces have a tendency to become encapsulated in fibrous scar tissue. The encapsulations are quite hard and in many instances frustrated the intended purpose of the prosthesis. As a consequence encapsulation sometimes requires a revision of the procedure. Such a revision means the implantation of another prosthesis. Unfortunately, this adds to patient distress and subjects the patient to the risks and expenses of the surgery for a second time.
In order to avoid or limit the scar tissue encapsulation problem, it has been found that an implant with a textured or roughened surface disorganizes the scar tissue and leads to improved results. Thus, silicone may be molded in geometric patterns on the outer surface of an implant to provide texturing as disclosed in U.S. Pat. No. 6,187,043 to Ledergerber. Silicone foam may also be employed for this purpose as disclosed in U.S. Pat. No. 4,859,712 to Cox.
More specifically, the Cox patent discloses a method for making a silicone skin for implantation where the overall density and depth of the foam may be carefully controlled beyond that possible when using chemical foaming agents. More specifically, crystalline material is embedded in a layer of uncured silicone. The silicone is then cured and a solvent is then used to dissolve the crystals out of the silicone thereby leaving an irregular surface. The size and amount of the crystals are varied to produce a desired surface texture or structure.
While the method disclosed in Cox is quite useful for customizing a silicone foam structure to meet the needs of any particular application, improvement is still possible. Specifically, the dissolving step and the step of subsequently drying or removing the solvent from the silicone foam are relatively time-consuming and therefore slow production rates. Further, it is necessary to recover the crystalline material from the solvent or continually provide a new source of crystalline material. Additionally, if the crystalline material is not recovered waste treatment is required in order to avoid contamination of the environment. The present invention relates to a method of producing a silicone foam which allows one to customize the foam to a particular application in a manner similar to that taught in the Cox patent yet totally avoids these other shortcomings.
In accordance with the purposes of the present invention as described herein an improved method is provided for producing silicone foam. The method includes the steps of adding a mechanical foaming agent in the form of a plurality of solid bodies to uncured silicone, curing the silicone and removing the mechanical foaming agent as intact solid bodies from the silicone thereby providing a silicone foam.
The method may be further defined as including the step of reusing the mechanical foaming agent to produce more silicone foam following the removing step. Further the method may include the selecting of the mechanical foaming agent from a group of materials consisting of metal, plastic, glass, cured silicone beads and mixtures thereof. Additionally, the solid bodies of mechanical foaming agent may have a width/diameter of between about 0.5 to about 8.0 mm. Further the mechanical foaming agent may be removed by pressing the solid bodies from the cured silicone foam.